Biology, Environment, Sea and ocean

How coral reefs are made?

This post’s subject is the formation of coral reefs. Are very delicate ecosystems which many marine species depend.

How they form?

Many little marine organism, known as coral polyps collect calcium and carbonate ions from sea to build an exoskeleton made of calcium carbonate (CaCO_{3}) for protection.

Ca^{2+}+CO_{3}^{2-}\rightarrow CaCO_{3}

The corals are from the Cnidaria phylum and Anthozoa class, the same phylum of jellyfishes. They measure around 1.5 cm.

The corals die and a new polyps generation grow up above calcium carbonate and the process continue for thousand of years, forming many carbonate calcium layers. This animation shows the coral reef’s formation, which are represented by the colors tan and purple.

[WPGP gif_id=”10212″ width=”600″]

Calcareous algae and some mollusks also participate in the reef construction. How the corals produce colors? Exists a symbiosis between the corals and microalgae called zooxanthellae. These microalgae live inside polyp’s tissues, make photosynthesis and provide nutrients to the corals. In exchange, the zooxanthellae lives from the nutrients coming from host’s metabolism and produce pigments to the later.

Some of these pigments can be fluorescents.

Types of coral reefs

Exist the following types of reefs.

  • Fringing: Grow next to the shore, it is formed from the beach and expands toward sea.

  • Barrier: With erosion, the beach falls back and a deep lagoon stays between the beach and the reef.

  • Atoll: Are circular in the middle of a salty lagoon which was an island before.

  • Patch: are isolated reef “islands”, can stay close to fringing, barriers and atolls.

A topological vision of the most known three types.

Where there are coral reefs?

Most of coral reefs can be found in waters with the following conditions:

  • Latitudes equal or lower than 30º;
  • Water temperature between 23ºC and 31ºC;
  • In the photic zone until 50 meters deep.

This map shows where stay the reefs in red pixels.

This post is not everything about coral reefs. Other posts about this subject will come.


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About Pedro Ney Stroski

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